This is the beginning of a nice facesitting session.
She starts with teasing her slave with her boots, then she steps over him and decends her ass.
Once she's sitting on his stomach and chest, she let him feel her full weight. (she is tall and for that she weighs alot)
Soon she moves on his throat and face, cutting off his breath supply.
With turrning around and sitting reverse, she does the same game... moving back until his face is under her ass.